1. Field of Art
This invention relates to a novel compound for the recovery and purification of palladium. More particularly, this invention relates to novel ortho alkoxy substituted phenyl oxime compounds which are capable of selectively separating and recovering palladium from aqueous compositions and mixtures containing palladium and other metal ions such as aluminum, nickel, iron, copper, other platinum family metals, rhodium, ruthenium, platinum and the like.
2. Prior Art
The recovery and purification of platinum group metals, such as palladium and platinum, is an important commercial process. For example, such processes are useful in the recovery of palladium from solutions obtained in the recovery of mineral deposits of the platinum metals, which solutions commonly contain in addition to palladium, ruthenium, rhodium, iridium and platinum, and small quantities of base metals such as iron, and nickel. Such processes are also useful in the recovery of palladium from spent catalyst materials, such as automobile catalytic converters.
Several extraction methods have been developed for recovery of palladium metal values. Solvent extraction processes for the recovery of metal values have certain well recognized advantages over other recovery methods, and such solvent extraction processes are increasing in number and types of applications. Fundamental to a successful solvent extraction process for the recovery palladium is the identification of a water immiscible composition (combination of compounds which will selectively bind to palladium and a suitable solvent) which will selectively extract palladium from an aqueous solution containing palladium, other platinum group metals and other metals. A further requirement for a successful palladium metal recovery by the solvent extraction techniques is an extracting composition having the property such that palladium metal values extracted by the extracting solvent can be recovered from same using another suitable aqueous phase.
Illustrative of such prior art solvent extraction processes are those described in U.S. Pat. No. 3,967,956 and in United Kingdom Pat. No. 20,136,443. In the processes of these patents, palladium is recovered from a mixture of palladium and other platinum group metals through use of an extracting composition containing ortho hydroxyoxime compounds, such as alkyl substituted ortho-hydroxyphenyl oxime compounds. The extracted palladium metal is removed from the extracting solvent by contacting same with a strongly acidic aqueous solution. This method is generally a useful procedure for recovering certain metals from the extracting solvent because the recovery procedure is pH dependent. With ortho-hydroxy phenyl oxime compounds, the extraction process is dependent on the ionizable nature of the phenolic hydrogen, and in the Cu.sup.+2 system is generally believed to follow the following equilibrium in which "LH" is the un-ionized oxime: ##STR1## Presumably, the Pd.sup.+2 system would operate in a similar manner when being extracted by ortho-hydroxy phenyl oxime compounds, In which case, palladium metal values are extracted into the organic water immiscible extracting solvent as the neutral species PdL.sub.2, while LH ionizes so that the acidity of the aqueous phase increases. Recovery by treatment with strong acid is effective because by shifting the equilibrium, the oxime is protonated releasing the palladium as Pd.sup.+2 which migrates into the polar aqueous phase.